Effects of Irrigation Regimes and Nitrogen Levels on Morphophysiological Traits and Yield of Hybrid Maize in a Sandy Loam Soil

Background and Objectives
Maize (Zea mays L.), belonging to the Poaceae family, is one of the four major cereal crops worldwide and plays a vital role in food security and livestock feed. In Iran, the cultivated area of maize exceeds 139,000 hectares, with a reported production of 962,000 tons. Optimal use of chemical inputs, such as nitrogen fertilizers, can increase corn yield by up to 60%. Maize is highly sensitive to nitrogen deficiency, which can reduce grain yield by up to 70%. Nitrogen directly affects the number of ears, kernel size, and protein content. The response of maize to nitrogen is influenced by factors such as cultivar, irrigation, and climatic conditions. Drought stress is one of the most significant yield-limiting factors in maize, disrupting physiological and morphological processes. Water stress leads to a reduction in photosynthesis, protein synthesis, and chlorophyll content. Plants activate mechanisms such as osmotic adjustment and accumulation of soluble sugars to cope with drought stress. Compared to some other crops, maize has a higher capacity for osmotic regulation and maintaining stomatal efficiency. The water requirement of maize depends on the irrigation method, soil type, and cultivar. Proper nitrogen management under water deficit conditions plays a key role in improving yield. This study investigates the effects of different nitrogen levels and irrigation regimes on the morpho-physiological traits of hybrid maize 703 to provide optimal strategies for sustainable agriculture in arid regions.
Materials and Methods
This research was conducted in 2019 at the Agricultural Research Center of Jiroft, located at 28.5464° N latitude, 57.8586° E longitude, and an altitude of 630 meters above sea level. The experiment was arranged as a split-plot design based on a randomized complete block design with three replications. The two factors were irrigation at four levels of 90, 140, 190, and 240 mm evaporation from a Class A pan and nitrogen fertilizer at four levels of 200, 300, 400, and 500 kg urea per hectare. Hybrid maize 703 was sown on August 11, 2019, with row spacing of 75 cm and plant spacing of 20 cm. Nitrogen fertilizer was applied in two stages: at the four-leaf stage and at flowering, each with 50% of the total amount. Morphological traits (plant height, stem diameter), yield components (number of ears, thousand-kernel weight, grain yield), and physiological traits (chlorophyll a, b, and carotenoid contents) were measured. Data were analyzed using SAS software version 9.4, and means were compared using Duncan’s multiple range test at the 5% probability level.
Results
Analysis of variance showed that ear length was affected only by irrigation stress, with a significant reduction as the stress increased from 90 to 240 mm evaporation. Ear diameter and cob weight were influenced by the interaction of irrigation and nitrogen, with the highest cob weight (70 g) observed in the 140 mm evaporation and 500 kg nitrogen treatment, and the lowest (22 g) in the 140 mm and 300 kg nitrogen treatment. Yield components such as kernel weight per ear, number of kernels per row, and kernel diameter were also significantly affected by the irrigation × nitrogen interaction. The highest kernel weight was recorded at 140 mm with 500 kg nitrogen, and the greatest number of kernels per row (46.3) at 90 mm with 500 kg nitrogen. The number of kernel rows was influenced solely by nitrogen, with 400 and 500 kg levels resulting in a significant increase. Fresh ear weight was also affected by the interaction of the two factors, with the highest value (150 g) observed at 90 mm with 500 kg nitrogen. Regarding vegetative traits, plant height and stem diameter were significantly influenced by the irrigation × nitrogen interaction, with the tallest plants (190.6 cm) and thickest stems recorded in the 90 mm and 500 kg nitrogen treatment. Chlorophyll a and total chlorophyll content were significantly affected by the interaction of factors, with the highest values (18.3 and 18.72 mg per g fresh leaf weight, respectively) observed in the 90 mm and 500 kg nitrogen treatment. Chlorophyll b content was only affected by irrigation and decreased with increasing drought stress. Grain and biological yields were significantly affected by the interaction of factors, with the highest values obtained in the 90 mm and 500 kg nitrogen treatment. Harvest index was highest in the 140 mm and 500 kg nitrogen treatment. The 100-kernel weight was also influenced by the interaction of factors, with the highest value (25.36 g) observed in the 90 mm and 500 kg nitrogen treatment.
Conclusion
Overall, the application of 500 kg nitrogen per hectare combined with irrigation based on 90 mm evaporation from a Class A pan provided the best conditions for maize growth and yield. Based on these results, it is recommended to avoid water stress exceeding 140 mm evaporation for hybrid maize 703 planted in a sandy loam soil in the Jiroft region, Kerman province, and optimal nitrogen application can mitigate the adverse effects of water deficit. Also the findings indicate that under conditions of sufficient water supply, nitrogen fertilizer use can be reduced by about 50% without a significant decrease in yield. Such results are of great importance from an economic and environmental perspective.
Author Contributions
Conceptualization, M.T., A.R., S.A.H., and M.E.; methodology, M.T. and M.E.; field investigation, M.T. under the supervision of M.E.; data analysis, M.T. with guidance from A.R., S.A.H., and M.E.; writing—original draft preparation, M.T.; writing—review and editing, A.R., S.A.H., and M.E.; supervision, A.R.; project administration, A.R.; manuscript preparation and submission, M.E. All authors have read and agreed to the published version of the manuscript.
Data Availability Statement
Data is available on reasonable request from the authors.
Acknowledgements
This paper is part of an M.Sc. thesis conducted at the Faculty of Agriculture, Vali Asr University of Rafsanjan, Iran. The authors gratefully acknowledge the Research Center of Agriculture and Natural Resources of Southern Kerman, Jiroft, Iran, for providing field facilities and technical support.
Conflict of interest
The authors declare no conflict of interest.
Ethical considerations
The authors avoided data fabrication, falsification, plagiarism, and misconduct.